Well, I have good news, and I have bad news. 

I didn't take nearly as many photos as I would have liked, but I did get some nice macro shots of the daughter board and mother board pre- and post-resistor changes. Cleaning the old heatsink compound was easy (just rub it off with your finger!). Taking apart the case was an adventure as I wasn't 100% sure how certain pieces came off. But, alas, I was able to completely disassemble my Dual 867MHz (133MHz bus) MDD Power Mac G4 and turn it into a Dual 1.08GHz (167MHz bus) model.

Fans... This is the fun part, really. The 80mm fan I bought blows the wrong direction. I either have to duct tape (hopefully not literally) to face the other way, or I might be able to leave its chasis as is and turn the fan itself around. I'm going to look into that later. The 60x25 fans I bought for the PSU are hopefully strong enough. Modding them to work (removed a wire, sliced the rubber noise dampeners off of the old ones and glued them to the new ones) was very easy. I'd also like to express that opening the power supply is not scary, but maybe it had discharged after a few hours of not being on.

The copper heatsink is definitely not limited to the FW800 versions of the MDDs. It fits just fine on a FW400 model, and applying the thermal compound goo was not as difficult as I thought. I was really afraid I'd either over-do that or that the soldering work from earlier would get done wrong.

I put two of the same kind of the 60x25 fans behind the copper heatsink, not knowing yet that the 80mm fan would be blowing the wrong way. That's not even the big issue... Those "quiet, low air flow" fans are SO INCREDIBLY LOUD. It's like I'm vaccuuming with my computer. So, question: How can I reduce the voltage coming through the power lead these fans are connected to?

The 80mm fan proved to be a BIG problem. Changing its cables back and forth between its original connector and the old fans' resulted in broken power-cable ends. A little wire binding provided the ones from the old fan and it... Sort of worked. Apparently, the fan I bought can't be properly powered by the lead supplied specifically for the 80mm fan! So, it and the two fans behind the heatsink are all going off the same HDD lead (from the third and fourth HDD spot). Oh, I removed that second hard drive chasis and ribbon cable as they were unused.

Next question: What's a good way to gain access to the second power lead in the optical drive chasis? The sliding shielding piece pretty much denies me access. Should I just cut out one corner to allow the lead to dangle out? I don't actually need, and may never, but it'd be good to know if that's OK to do. I don't want to remove the shielding all together.

The 60x15 fan that blows on the optical drives wouldn't work until I switched it to have the old fans 2-pin connector, despite the 3-pin-wide (only two wires) connector fitting on just fine. Weird. That fan also had to have its four mounting holes drilled out bigger. The two rods that it slides down on are wider than stock fan hole sizes. Hurray!

Oh, the 60x25 fans behind the heatsink run the same speed with or without the third (yellow) wire. Just, FYI.

I'm still looking at mounting my remaining two 60x25 fans into the bottom-front of the case, outside the grill that sits below the first two hard drive bays. They would be placed to pull air into the case, towards the main fan, which in an ideal world would then blow across the heatsink and have that hot air pulled out the back by the last two fans. However, until I can find a way to cut down the voltage going to these fans, there's no way I'm adding more.

Without them, the machine seems fairly quiet.

Temperatures: Prior to all of this, the CPUs would get up to the low 50's (Celsius) pretty quickly. Now the computer cold boots at about 25°C and then steadily climbs to the mid-40's before the rate at which the temperature rises slows. I'm afraid to use it for more than 45 minutes to an hour at a time until the 80mm fan is blowing the right direction! The highest temperature on the original set-up that I ever saw was 58.1°C.

By, the way, third question: What is the third wire on most fans used for?

Performance: Got me. Because I won't let this computer run for extneded periods of time until the air flow is fixed, I'm not going to run any benchmarks or play World of Warcraft or use Photoshop to see how it's doing. It boots FAST, but it pretty much always did. Typing in these forums is a little laggy, but typing in TextEdit or Adium is super-responsive. This isn't the first time I've noticed a text field on a web page perform poorly.

Memory: The 2x1GB Princeton PC-3200 2-3-2-5 memory modules I bought are showing up as PC-2600, same way the x512MB Crucial CL 2.5 memory did BEFORE the bus speed increase.

Oddities: The first two hard drive bays' ribbon connects to the motherboard on what is labeled as an ATA-66 connection, despite the supposed ATA-100 performance. The optical drive is marked as ATA-33 on the mobo and I couldn't find any meaningful text on the connection for the other two drives.

Re-assemblinf the computer was a breeze. I'll see if I can take a couple extra photos of the post-assembly machine and maybe of any mods I make to the 80mm fan. I thought about using Photoshop to create actual images of the different resistor configurations for things, but then because I didn't have a tri-pod, decided not to try and somehow stop shaking enough to get clear enough macro shots of all the different parts of the mobo.

What I need now: Aside from cutting voltage to two (and eventually four) of the fans? Cable wraps! There's a mess of wires shoved into my system that are assuredly going to get caught in something someday.

In 32 minutes my CPU temperature has climbed to 48.1°C. The Maxtor 200GB HDD started at like 19°C and is now 35.0°C. I have not yet flashed my Radeon 9800 Pro, and I'm rather excited to see whether or not it also has temperature sensors that Temperature Monitor can read.

OK. Haphazard, stream-of-consciousness status report is now over.

-m

PS: Big ups to my dad for the soldering work, work bench, awesome screw driver set, and other tools and goodies that aided in this.

I would run your fans on a separate fan controller.  Then you can adjust for sound/temp.  Not having fans plugged into the motherboard is ok, as I run all of my fans (Killer Bee mod) on a controller.  As for you wrongly blowing fan.....cant you just turn it around?  If not, by a different one.  As for the psu, that beast always runs hot.  The third line on a fan is for sending fan speeds to a controller.  You dont have to have one.  To get more power connections, just add a molex splitter(molex female to two molex males).  They are cheap from any online mod joint. 

Is the cpu temp lower than before?  Max is 62C.  For example, mine is at 45.8C and never really goes above that.  Remember that it is not in the stock apple case which is a nice aesthetically, but is cooled like wearing a plastic bag on your head and trying to breathe.

Ah, a fan controller... Good idea! Haha. Thanks, maestro. I'm going to shut down now and see about finding a way to turn the 80mm around. Otherwise, yeah, I'll buy a new one.

OK... I rigged the 80mm fan to blow the other direction. It could only slide into the old fan's spot one way, so I turned it around regardless, jammed screws into the holes it had to put the old grill/cover on, and then used electrical tape to secure it down. It works! Hahaha.

I tried throwing in a Radeon 9800 Pro. Granted, I didn't tape the 3 and 11 pins, but the machine won't boot at all with it in. One thing that freaked me out was I installed the card into the AGP slot with the computer still connected to the wall (ie, power) but turned off. And it turned on! And then it beeped at me, which I knew meant something was wrong. With or without the 9800 getting its extra power source, the only way I could power down the system was by yanking the plug. It's back to it's 9000 Pro (AGP 4x) and working fine.

Now to look for fan controllers... And maybe a stronger power supply?!

OK... New info!

I've got my 9800 Pro taped and ready to be flashed, except that I apparently can't run the ATI Multi Flasher, even from a safe boot on 10.4. Is it because I don't have any of the OS 9 drivers (or OS 9) installed? Hmm.

Fortunately, I now have a second MDD (another DUal 867) loaded with hard drives (such that, if my room mate/cousin-in-law moves out, I'll have a sweet little RAID going) that I can slap a whole lot of different OSes on and do the flashing there.

All this time, my 200GB ATA133 Maxtor drive that I boot from has been on the ATA66 bus. So, I switched it over to the ATA100 bus only to learn that there's something horribly wrong with it. I freaked out. My computer was crashing about 1-3 minutes after booting consistantly and only holding the power button down would remedy the situation. After pacing and panicking for an hour, I moved it back to the ATA66 bus and here I am... Everything's fine.

So, all in all, my only complaints about this computer and my mod work: Lack of wire management; lack of working ATA100 bus; lack of fan controller; and apparent lack of ability to flash a video card. Now all I need are two power cables for the new MDD and its monitor. I can just go buy any generic power cable, right? They all seem to be the same. Except my iMac DVse power cable, which has numbers written on it that don't seem to match the PowerMacs...

By the way, I have no plans to mod the new Dual 867.

Knowing how much I procrastinate, and considering that my work isn't done, don't expect a mod guide/article from me anytime soon. 

Okay, couple things.  You need to flash the 9800 in a PC, as it is a PC card right?  And you will need a second video card to see what you are doing.  The tape mod can be very tricky and may take a few tries.  The power supply should be fine.  I am running 3x250gb, usb 2.0 pci, sata pci, fan controller, 3x120 fans, a flashed 9800xt, and a dvd burner.  No problemo.  Any computer power cable will work, I dont even use Apple ones cuz they are white.  Did you see my mod guides?  I have done 3 on the mdds.

I was under the impression that I could flash the 9800 in a Mac so long as I had a PCI video card to hook my display up to, and had the appropriate versions of Grapphiccelerator, ATI Multi Flasher, and the necessary ROM(s).

I haven't yet ordered a fan controller, but I'm with you on the black power cords. White = blech.

What else... Oh! So when I tried to flash the 9800 I had booted up while holding down shift. Possibly the combination of that and discovering my bum ATA100 connection (port?), I also discovered that OS X wasn't booting properly from that point on. It never gets to the blue OS X loading screen where it tells you what's being loaded up in the white box. It goes grey screen with Apple logo for a bit, then straight to the desktop.

I also can't put my computer to sleep by any means as it will not wake up. What have I done?!  :-[

Come to think of it, you may be able to flash a card in the mac.  Anyway, did you repair permissions?  Problems with the OS can usually be fixed that way.  You may find that the ata/100 connection works then to.  By the way, always back up before delving into uncharted territory!

I booted from a 10.4.3 install DVD and repaired permissions. I got one good use of the system after putting the drive back on the ATA66 connection, repaired permissions again, and now it's all screwed up. I'm going to put the drive in the "new" MDD I got and back it up atfer some time-consuming drive swapping. (iMac's not-even-close-to-filled 80GB to a 60GB, MDD's 200GB - also hardly filled - to the 80GB, and put 10.4.7 and 9.2.2 on the other 60GB) and work from there. Once the 200GB is backed up, I'm willing to do just about anything to that drive.

I haven't yet tested the machine with one memory stick or with the 4x512MB PC2700 Crucial set up it had before the OC. I don't think this is a heat issue, as the temp sesnors seem to be working fine and when the machine ran properly, I never even saw it hit 50 degrees (Celsius). Could it be a power issue? I wonder if the 80mm fan I put in is screwing with things since it seems to require more power - it wouldn't work on the mobo's 2-pin connector that the old 80mm fan was on as that connector did not supply enough power. I would think if it was a heat issue then it would shut down, not crash. And, I would also think that if there was a power issue, it wouldn't boot or boot properly.

After backing, I'll run a series of light testes/repairs (the log-cleaning cron jobs, repairing permissions, fsck, and anything else I can think of) and then try hardware testing (changing RAM, maybe taking out the extra two fans).

I need to get to the bottom of this or I'm out $700.  :'(

By the way, the new MDD has a totally different heatsink than the first one I got. Both are/were Dual 867s. It also has a different PSU and main (80mm) fan, but I fully expected that.

One more quick bit of info: Around the same time as these hard crashes started, I had done with PRAM reset (Command+Option+P+R) a couple of times. I don't know why. I just thought it might not be a bad idea since some elements of the system had changed.